A new perspective on the stellar Mass-Metallicity Relation of quiescent galaxies from the LEGA-C survey

The elemental abundance of galaxies holds fundamental information on how they formed and evolved. In particular, the stellar metallicity of a galaxy is tightly related to its Star Formation History (SFH), being the consequence of the interplay between how quickly its stars produce and release metals in the interstellar medium, and how much of these metals are retained and reprocessed into new stars. In the local Universe, galaxies exhibit a positive correlation between their stellar mass and metal content. This is known in the literature as the Mass-Metallicity Relation (MZR), which indicates that more massive galaxies are, on average, more metal-rich than less massive ones. Making use of the Large Early Galaxy Assembly – Census (LEGA-C) survey, we studied the stellar population properties of a large (>600) sample of quiescent galaxies at intermediate (0.6 <= z <=1) redshifts. In particular, we investigated the stellar MZR and noted that the average trend is not fully representative of the whole population. Indeed, while most massive galaxies are always metal-rich, lower-mass galaxies can have both low metallicities and metallicities as high as the most massive galaxies. However, this information gets overlooked when focusing solely on the average trend. In this talk, I will present a new perspective on the MZR and I will show that both observations and simulations support our interpretation. Further, I will discuss the dependence of the stellar mass and metallicity of quiescent galaxies on their SFHs, formation times, and [alpha/Fe] abundances.